Constant velocity universal joint outer joint member and manufacturing method for same

ABSTRACT

In an outer joint member of a constant velocity universal joint, a cup member and a shaft member are made of medium to high carbon steel and welded together. The cup member has a bottomed cylindrical shape that is opened at one end, and includes a cylindrical portion, a bottom portion, and a short shaft section of a solid shaft shape protruding from the bottom portion and having a joining end surface. The shaft member has a solid shaft shape and a joining end surface. The joining end surfaces of the cup and shaft members are brought into abutment against each other, and a high energy intensity beam is radiated from an outer side in a radial direction to form a welded portion. A structure of a molten metal at the welded portion is in a mixed phase of ferrite and granular cementite.

TECHNICAL FIELD

The present invention relates to an outer joint member of a constantvelocity universal joint and a method of manufacturing the outer jointmember. More specifically, the present invention relates to an outerjoint member of a joint type manufactured by welding a cup member and ashaft member to each other, and a method of manufacturing the outerjoint member.

BACKGROUND ART

In a constant velocity universal joint, which is used to construct apower transmission system for automobiles and various industrialmachines, two shafts on a driving side and a driven side are coupled toeach other to allow torque transmission therebetween, and rotationaltorque can be transmitted at a constant velocity even when each of thetwo shafts forms an operating angle. The constant velocity universaljoint is roughly classified into a fixed type constant velocityuniversal joint that allows only angular displacement, and a plungingtype constant velocity universal joint that allows both the angulardisplacement and axial displacement. In a drive shaft configured totransmit power from an engine of an automobile to a driving wheel, forexample, the plunging type constant velocity universal joint is used ona differential side (inboard side), and the fixed type constant velocityuniversal joint is used on a driving wheel side (outboard side).

Irrespective of the fixed type and the plunging type, the constantvelocity universal joint includes, as main components, an inner jointmember, an outer joint member, and torque transmission members. Theouter joint member includes a cup section and a shaft section. The cupsection has track grooves formed in an inner peripheral surface thereofand configured to allow the torque transmission members to roll thereon.The shaft section extends from a bottom of the cup section in an axialdirection. In many cases, the outer joint member is constructed byintegrally forming the cup section and the shaft section by subjecting arod-like solid blank, that is, a round bar to plastic working such asforging and ironing or processing such as cutting work, heat treatment,and grinding (see FIG. 4 and FIG. 8 of Patent Literature 1).

Incidentally, an outer joint member (long stem type) including a shaftsection longer than a standard may sometimes be used. For example, inorder to equalize lengths of a right part and a left part of the driveshaft, the long stem type is used for a constant velocity universaljoint on the inboard side that corresponds to one side of the driveshaft. In this case, the shaft section is rotatably supported by asupport bearing. Although varied depending on vehicle types, the lengthof the shaft section of the long stem type is approximately from 300 mmto 400 mm in general. The outer joint member of the long stem type has along shaft section, and hence there is a difficulty in integrallyforming the cup section and the shaft section with high accuracy.Therefore, there is known an outer joint member in which the cup sectionand the shaft section are formed as separate members, and both themembers are joined through friction press-contact (Patent Literature 2).

An overview of the friction press-contact technology for the outer jointmember described in Patent Literature 2 is described below. First, asillustrated in FIG. 27, a cup member 72 and a shaft member 73 are joinedthrough the friction press-contact to form an intermediate product 71′.Next, burrs 75 on a radially outer side of a joining portion 74 areremoved, and hence an outer joint member 71 as illustrated in FIG. 28 isobtained. The burrs 75 are generated on the joining portion 74 of theintermediate product 71′ along with the press-contact. The burrs 75 onthe radially outer side of the joining portion 74 are removed throughprocessing such as turning. Accordingly, a support bearing (rollingbearing 6: see FIG. 1) to a shaft section of the outer joint member 71.

Although illustration is omitted, the intermediate product 71′ isprocessed into a finished product of the outer joint member 71 throughmachining of a spline, snap ring grooves, and the like, and through heattreatment, grinding, and the like. Therefore, the outer joint member 71and the intermediate product 71′ have slight differences in shape.However, illustration of the slight differences in shape is omitted inFIG. 27 and FIG. 28 to simplify the description, and the outer jointmember 71 being the finished product and the intermediate product 71′are denoted by the reference symbols at the same parts. The same appliesto the description below.

CITATION LIST

Patent Literature 1: JP 11-179477 A

Patent Literature 2: JP 2012-057696 A

Patent Literature 3: JP 05-208280 A

SUMMARY OF INVENTION Technical Problem

The burrs 75 on the joining portion 74, which are generated due to thefriction press-contact, not only are quenched by friction heat andcooling that follows the friction heat to have a high hardness but alsohave a distorted shape extended in an axial direction and a radialdirection. Therefore, when removing the burrs 75 on the radially outerside through the turning, a tip for turning is liable to besignificantly abraded due to the high hardness and cracked due to thedistorted shape. Therefore, it is difficult to increase the turningspeed. In addition, a cutting amount per pass of the tip for turning isdecreased, and hence the number of passes is increased, which causes aproblem in that the cycle time is increased to increase themanufacturing cost.

Further, in order to inspect a joining state of the joining portion 74of the outer joint member 71, when ultrasonic flaw detection, whichenables flaw detection at high speed, is to be performed, an ultrasonicwave is scattered due to the burrs 75 remaining on the radially innerside of the joining portion 74, and hence the joining state cannot bechecked. Therefore, there occurs a problem in that total inspectionthrough the ultrasonic flaw detection cannot be performed after thejoining.

In view of the above-mentioned problems, when welding through use ofhigh energy intensity beam such as laser welding or electron beamwelding is employed, it is conceivable that the surfaces of the joiningportion may be prevented from being increased in thickness unlike thecase of the friction press-contact. However, as illustrated in FIG. 29,when the cup member 72, which has a hollow cavity portion that extendsin an axial direction from a joining end surface, and the shaft member73 are brought into abutment against each other to be welded, a hollowcavity portion 76 having a relatively large volume is formed. Then, apressure in the hollow cavity portion 76 is increased due to processingheat during the welding, and after completion of the welding, thepressure is decreased. Due to such variation in the internal pressure ofthe hollow cavity portion 76, blowing of a molten material occurs. Thus,there arise defects such as formation of a recess on a surface of thewelded portion, poor penetration depth, and generation of air bubblesinside the welded portion, thereby degrading the welding state. As aresult, the strength of the welded portion is not stable, whichadversely affects quality.

Further, the following problems have been found during the course ofpursuing quality and reliability of the welded portion through electronbeam welding in terms of production technology. That is, it is necessaryto improve a welding method in order to establish productivity of aconstant velocity university joint being a mass-produced product forautomobiles and the like. Specifically, an outer diameter at the joiningportion of the outer joint member of the constant velocity universaljoint to be applied to a drive shaft for automobiles is approximatelyfrom 40 mm to 60 mm, and the joining portion between the cup member andthe shaft member through abutment has a substantially solid form. Insuch a solid form, a mass is large, and hence the welded portion israpidly cooled by self-cooling and brought into a quenched state. It hasbeen found that a large amount of input heat is required in order toprevent such a state by pre-heating. Therefore, it is necessary to takemeasures in consideration of conditions for productivity of a constantvelocity universal joint being a mass-produced product for automobilesand the like.

The cup member and the shaft member constructing the outer joint memberof the constant velocity universal joint employ medium to high carbonsteel having a high carbon content to secure strength. Thus, when thecup member and the shaft member are welded to each other as they are,the welded portion is significantly hardened, and becomes more liable tobe cracked. For example, in the case of carbon steel for a machinestructure having a carbon content of 0.45% (S45C), the hardness of themartensite exceeds 700 HV. Therefore, for the purpose of reducing thehardness and securing toughness, it is conceivable to performpre-heating to reduce the cooling speed after welding.

As a method of pre-heating, for example, in the laser welding,pre-heating can be performed through short-time heating with highfrequency waves. However, in the case of the electron beam welding,welding is performed in vacuum, and hence there is a difficulty ininstallation of a high frequency wave heating device. Thus, pre-heatingis performed through use of an electron beam. However, the electron beamhas a small heat input range. Thus, heat dissipation during pre-heatingis significant during welding for a workpiece having a large volume.Accordingly, there is a problem in that pre-heating requires a longperiod of time, thereby extending the cycle time for welding.

Further, as another method which offers a similar effect, there is amethod using post-heating as described in Patent Literature 3. Thewelding method described in Patent Literature 3 includes sandwiching amember to be welded between electrodes, allowing a welding current toflow therethrough to weld the joining portion, and thereafterintermittently and repeatedly adding a current which is lower than thewelding current to have slower cooling at the welding portion. However,when this welding method is to be employed in the electron beam welding,a device needs to be added, and the period of time required forpost-heating is also extended.

It is an object of the present invention to prevent a crack at a weldingportion of an outer joint member of a constant velocity universal jointwhich is manufactured through welding of a cup member and a shaft memberto each other.

Further, the present invention is to provide a method of manufacturingthe outer joint member of the constant velocity universal joint which isprevented from cracking at the joint portion between the cup member andthe shaft member, without extending a welding cycle time.

Solution to Problem

In order to solve the above-mentioned problems, according to oneembodiment of the present invention, there is provided an outer jointmember of a constant velocity universal joint, the outer joint membercomprising:

a cup section having track grooves formed at an inner periphery of thecup section and configured to allow torque transmitting elements to rollthereon; and

a shaft section formed at a bottom portion of the cup section,

the outer joint member being constructed by forming the cup section andthe shaft section through use of separate members, and by welding a cupmember forming the cup section and a shaft member forming the shaftsection,

the cup member and the shaft member being made of medium to high carbonsteel (carbon content of 0.25 mass % or more),

the cup member having a bottomed cylindrical shape that is opened at oneend, and comprising a cylindrical portion, a bottom portion, and a shortshaft section of a solid shaft shape protruding from the bottom portionand having a joining end surface at an end portion,

the shaft member having a solid shaft shape and having a joining endsurface at one end thereof,

the joining end surface of the cup member and the joining end surface ofthe shaft member being brought into abutment against each other, a highenergy intensity beam being radiated from an outer side in a radialdirection to form a welded portion, and a structure of a molten metal ata welded portion being in a mixed phase of ferrite and granularcementite.

The molten metal at the welded portion is formed into a martensite byrapid cooling after welding, and the martensite is eliminated bypost-heating, thereby forming a mixed layer of ferrite and cementite.This is a microstructure from which fine granular cementite isprecipitated, which is known as a so-called tempered structure.

The welded portion is a generic name of a portion including a weldedmetal and a heat-affected portion. The welded metal is metal which formspart of the welded portion and is molten and solidified during welding.The heat-affected portion is a portion which is changed in structure,metallurgical property, mechanical property, and the like by heat ofwelding and is unmolten part of a base material (JIS Z 3001-1 WeldingTerms—Section 1: General).

Herein, the term “solid shaft shape” is intended to exclude a shafthaving a hollow cavity penetrating in an axial direction, e.g., a hollowshaft using a pipe, or a shaft having an elongated hollow cavity portionextending from a joining end surface in the axial direction (see PatentLiterature 2). The cup member has a bottomed cylindrical shape as awhole, but the short shaft section having the joining end surface formedthereon does not have a through hole and an elongated hollow cavityportion extending from the joining end surface in the axial direction.Thus, at least the short shaft section has a solid shaft shape.

According to one embodiment of the present invention, there is provideda method of manufacturing the outer joint member of the constantvelocity universal joint comprising: performing pre-heating beforeradiating a high energy intensity beam for welding to input heat to ajoining portion; and performing post-heating after welding to reduce acooling rate for the welded portion.

Through employment of post-heating in addition to pre-heating, inputheat generated during welding can be utilized in post-heating.Therefore, a required input heat amount can be secured even with a shortpre-heating time, thereby being capable of reducing the welding cycletime as a whole as compared to the case of employing only pre-heating.

Advantageous Effects of Invention

According to the present invention, welding is performed after heatinput through pre-heating, and post-heating is performed after welding.With this, the structure formed into the martensite by rapid coolingafter welding loses the martensite by post-heating and is formed into amixed layer of ferrite and cementite. This is a microstructure fromwhich fine granular cementite is precipitated, which is known as theso-called tempered structure. Thus, with the tempering effect offered bypost-heating, the hardness of the molten metal at the welded portion isreduced, thereby being capable of not only preventing a crack but alsosecuring toughness.

Further, during post-heating, input heat accumulated in a workpieceduring welding may be utilized. Accordingly, the input heat amountrequired for raising temperature may be less than the case of performingonly pre-heating, thereby being capable of reducing the welding cycletime.

In welding with a high energy intensity beam, a bead width is small, anddeep penetration can be obtained in a short period of time, therebybeing capable of increasing the strength of the welded portion andreducing thermal strain. Further, burrs are not generated, and hencepost-processing for the joining portion can be omitted. As a result, themanufacturing cost can be reduced. Further, there is no scattering ofultrasonic waves caused by the burrs, which is a problem raised in thecase of joining through the friction press-contact. Thus, totalinspection through ultrasonic flaw detection can be performed to stablysecure high welding quality. Further, in general, the electron beamwelding is performed in vacuum. Therefore, even when a hollow cavityportion is present in the welded portion, the problems such as theblowing of a molten material and the generation of air bubbles are lessliable to occur.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a partial sectional front view of a drive shaft including aplunging type constant velocity universal joint with an outer jointmember of a long stem type.

FIG. 2a is an enlarged view for illustrating a first embodiment of theouter joint member of FIG. 1.

FIG. 2b is an enlarged view of a portion “b” of FIG. 2 a.

FIG. 2c is an enlarged view, which is similar to FIG. 2b , forillustrating a state before welding.

FIG. 3 is a block line diagram for illustrating manufacturing steps forthe outer joint member of FIG. 1.

FIG. 4a is a vertical sectional view of a cup member after ironing.

FIG. 4b is a vertical sectional view of the cup member after turning.

FIG. 5a is a front view of a bar material being a blank of a shaftmember.

FIG. 5b is a partial sectional front view after forging.

FIG. 5c is a partial sectional front view of the shaft member afterturning and spline processing.

FIG. 6 is a schematic elevation view of a welding apparatus beforewelding.

FIG. 7 is a schematic elevation view of the welding apparatus duringwelding.

FIG. 8 is a schematic elevation view of an ultrasonic flaw-detectionapparatus.

FIG. 9 is a schematic plan view of the ultrasonic flaw-detectionapparatus.

FIG. 10 is a schematic elevation view of the ultrasonic flaw-detectionapparatus.

FIG. 11 is a schematic plan view of the ultrasonic flaw-detectionapparatus.

FIG. 12a is a partial enlarged sectional view taken along the lineXII-XII of FIG. 10 in a case of a non-defective welded product.

FIG. 12b is a partial enlarged sectional view taken along the lineXII-XII of FIG. 10 in a case of a defective welded product.

FIG. 13 is a partial enlarged sectional view, which is similar to FIG.12a and FIG. 12b , for illustrating findings in the course ofdevelopment.

FIG. 14 is a partial sectional front view for illustrating a shaftmember assigned with a different product number.

FIG. 15 is a partial sectional front view of an outer joint member thatis manufactured using the shaft member of FIG. 14.

FIG. 16 is a block line diagram for illustrating an example ofstandardization of a product type of the cup member.

FIG. 17a is a partial sectional front view for illustrating a secondembodiment of the outer joint member.

FIG. 17b is an enlarged view of a portion “b” of FIG. 17 a.

FIG. 17c is an enlarged view, which is similar to FIG. 17b , forillustrating a state before welding.

FIG. 18 is a vertical sectional view of the cup member of FIG. 17 a.

FIG. 19 is a block line diagram for illustrating a second embodiment ofa method of manufacturing an outer joint member.

FIG. 20 is a block line diagram for illustrating a third embodiment ofthe method of manufacturing the outer joint member.

FIG. 21 is a partial sectional front view for illustrating a constantvelocity universal joint of the third embodiment of the outer jointmember.

FIG. 22 is a partial sectional front view of the outer joint member ofFIG. 21.

FIG. 23 is a line graph for showing a welding heat history according toExample.

FIG. 24a is a microphotograph of a molten metal at a welded portionaccording to Example.

FIG. 24b is a schematic sectional view for illustrating a photographedpart.

FIG. 25 is a line graph for showing a welding heat history according toComparative Example.

FIG. 26a is a microphotograph of a molten metal at a welded portionaccording to Comparative Example.

FIG. 26b is a schematic sectional view for illustrating a photographedpart.

FIG. 27 is a vertical sectional view of an intermediate product of anouter joint member for illustrating a related art.

FIG. 28 is a vertical sectional view of the outer joint member forillustrating the related art.

FIG. 29 is a vertical sectional view of an outer joint member forillustrating another related art.

DESCRIPTION OF EMBODIMENTS

Now, description is made of embodiments of the present invention withreference to the drawings.

First, a first embodiment of an outer joint member is described withreference to FIG. 1 and FIG. 2a to FIG. 2c , and subsequently, a firstembodiment of a method of manufacturing the outer joint member isdescribed with reference to FIG. 3 to FIG. 16.

FIG. 1 is a view for illustrating the entire structure of a drive shaft1. The drive shaft 1 mainly comprises a plunging type constant velocityuniversal joint 10, a fixed type constant velocity universal joint 20,and an intermediate shaft 2 configured to couple both the joints 10 and20. The plunging type constant velocity universal joint 10 is arrangedon a differential side (right side of FIG. 1: hereinafter also referredto as “inboard side”), and the fixed type constant velocity universaljoint 20 is arranged on a driving wheel side (left side of FIG. 1:hereinafter also referred to as “outboard side”).

The plunging type constant velocity universal joint 10 is a so-calleddouble-offset type constant velocity universal joint (DOJ), and mainlycomprises an outer joint member 11, an inner joint member 16, aplurality of balls 41 serving as torque transmitting elements, and acage 44 configured to retain the balls 41.

The outer joint member 11 comprises a cup section 12 and a long shaftsection (hereinafter also referred to as “long stem section”) 13 thatextends from a bottom of the cup section 12 in an axial direction. Theinner joint member 16 is housed in the cup section 12 of the outer jointmember 11. Track grooves 30 formed along an inner periphery of the cupsection 12 of the outer joint member 11 and track grooves 40 formedalong an outer periphery of the inner joint member 16 form pairs, andthe balls 41 are arranged between the track grooves 30 and 40 ofrespective pairs. The cage 44 is interposed between the outer jointmember 11 and the inner joint member 16, and is held in contact with apartially cylindrical inner peripheral surface 42 of the outer jointmember 11 at a spherical outer peripheral surface 45 and held in contactwith a spherical outer peripheral surface 43 of the inner joint member16 at a spherical inner peripheral surface 46. A curvature center O₁ ofthe spherical outer peripheral surface 45 and a curvature center O₂ ofthe spherical inner peripheral surface 46 of the cage 44 are offsetequidistantly from a joint center O toward opposite sides in the axialdirection.

An inner ring of a support bearing 6 is fixed to an outer peripheralsurface of the long stem section 13, and an outer ring of the supportbearing 6 is fixed to a transmission case with a bracket (not shown). Asdescribed above, the outer joint member 11 is supported by the supportbearing 6 in a freely rotatable manner, and hence vibration of the outerjoint member 11 during driving or the like is prevented as much aspossible.

The fixed type constant velocity universal joint 20 is a so-calledRzeppa type constant velocity universal joint, and mainly comprises anouter joint member 21, an inner joint member 22, a plurality of balls 23serving as torque transmitting elements, and a cage 24 configured toretain the balls 23. The outer joint member 21 comprises a bottomedcylindrical cup section 21 a and a shaft section 21 b that extends froma bottom of the cup section 21 a in the axial direction. The inner jointmember 22 is housed in the cup section 21 a of the outer joint member21. The balls 23 are arranged between the cup section 21 a of the outerjoint member 21 and the inner joint member 22. The cage is interposedbetween an inner peripheral surface of the cup section 21 a of the outerjoint member 21 and an outer peripheral surface of the inner jointmember 22.

Note that, as the fixed type constant velocity universal joint, anundercut-free type constant velocity universal joint may sometimes beused.

The intermediate shaft 2 comprises spline (including serrations; thesame applies hereinafter) shafts 3 on both end portions thereof. Thespline shaft 3 on the inboard side is inserted to a spline hole of theinner joint member 16 of the plunging type constant velocity universaljoint 10. Thus, the intermediate shaft 2 and the inner joint member 16of the plunging type constant velocity universal joint 10 are coupled toeach other to allow torque transmission therebetween. Further, thespline shaft 3 on the outboard side is inserted to a spline hole of theinner joint member 22 of the fixed type constant velocity universaljoint 20. Thus, the intermediate shaft 2 and the inner joint member 22of the fixed type constant velocity universal joint 20 are coupled toeach other to allow torque transmission therebetween. Although theexample of the solid intermediate shaft 2 is illustrated, a hollowintermediate shaft may also be used.

Grease is sealed inside both the constant velocity universal joints 10and 20 as a lubricant. To prevent leakage of the grease or entry of aforeign matter, bellows boots 4 and 5 are respectively mounted to aportion between the outer joint member 11 of the plunging type constantvelocity universal joint 10 and the intermediate shaft 2, and a portionbetween the outer joint member 21 of the fixed type constant velocityuniversal joint 20 and the intermediate shaft 2.

Next, details of the outer joint member 11 are described with referenceto FIG. 2a to FIG. 2 c.

The outer joint member 11 comprises the cup section 12 and the long stemsection 13. The outer joint member 11 is manufactured by joining the cupmember 12 a and the shaft member 13 a through butt welding, andmanufacturing steps are described later in detail.

The cup section 12 has a bottomed cylindrical shape that is opened atone end, and the inner peripheral surface 42 has the plurality of trackgrooves 30 that are formed equidistantly in a circumferential direction,thereby forming a partially cylindrical shape. The balls 41 (see FIG. 1)roll on the track grooves 30.

The cup member 12 a is an integrally-formed product being made of mediumcarbon steel, e.g., S53C, containing carbon of from 0.40 wt % to 0.60 wt%, and having a cylindrical portion 12 a 1 and a bottom portion 12 a 2.The cylindrical portion 12 a 1 has the track grooves 30 and the innerperipheral surface 42 described above. A boot mounting groove 32 isformed at an outer periphery of the cup member 12 a on the opening sidethereof, whereas a snap ring groove 33 is formed at an inner periphery.The bottom portion 12 a 2 has a shaft section having a solid shaft shapeprotruding toward the shaft member 13 a side, that is, a short shaftsection 12 a 3, and a joining end surface 50 (FIG. 2c ) is formed at theshort shaft section 12 a 3.

The joining end surface 50 is finished by turning. Herein, a shallowrecessed portion 50 b is formed on a radially inner side of the joiningend surface 50, and as a result, the annular joining end surface 50 isformed on a radially outer side of the recessed portion 50 b. Thereference symbol D denotes an inner diameter of the joining end surface50. The recessed portion 50 b may be formed during forging, or may beformed by cutting. When the recessed portion 50 b is formed duringforging, the number of steps can be reduced. Further, the joining endsurface 50 is formed into an annular shape, and hence time required forturning can be reduced.

The long stem section 13 is a solid shaft that extends from the bottomportion 12 a 2 of the cup section 12 in the axial direction. A bearingmounting surface 14 and a snap ring groove 15 are formed at an outerperiphery of the long stem section 13 on the cup member 12 a side,whereas a spline shaft Sp serving as a torque transmission couplingportion is formed at an end portion on a side opposite to the cupsection 12.

The shaft member 13 a is made of medium carbon steel, e.g., S40C,containing carbon of from 0.30 wt % to 0.55 wt %. A joining end surface51 (FIG. 2c ) is formed at an end portion on the cup member 12 a side.The joining end surface 51 has a recess 52, and as a result, is formedinto an annular surface. The reference symbol E denotes an innerdiameter of the joining end surface 51. FIG. 2a to FIG. 2c and FIG. 5ato FIG. 5c are illustrations of an example in which the recess 52 isformed during forging and in which the inner diameter portion 53 isformed in the joining end surface 51 by cutting. Thus, it appears as ifthe recess 52 and the inner diameter portion 53 are formed into a holehaving stages. However, the inner diameter portion 53 may be an innerdiameter portion of the joining end surface 51, or may be an innerdiameter portion of the recess 52. The recess 52 may maintain a forgedsurface. In that case, the inner diameter portion 53 that can be clearlydistinguished from the recess 52 does not appear as illustrated.

The recess 52 has a shallow bottom, that is, is very shallow withrespect to a diameter of the joining end surface 51. As an example ofthe depth, a lower limit is approximately 1 mm. That is intended tosecure a straight portion having a length in the axial directionnecessary to perform ultrasonic flaw detection for defectiveness indimension in the radial direction (penetration depth) of the weldedportion 49. The above-mentioned lower limit is a value in view of theultrasonic flaw detection. In view of reducing the pre-heating timethrough reduction of a volume near the joining portion, a correspondingdepth of the recess 52 is desired.

In the case of forming the recessed portion during forging, an upperlimit of the depth of the recess 52 is approximately a limit valueformed through forging (reference)×1.5 mm. Excessively deep recess 52may cause increase in forging load, degradation of die lifetime, andincrease in processing cost. Even in the case of forming throughcutting, excessively deep recess 52 may cause longer processing time andpoor material yield.

The inner diameter portion 53 of the joining end surface 51, while beingdependent on the outer diameter of the shaft member 13 a, is presupposedto secure a radial width of the welded portion 49 to be formed on theouter diameter side of the recess 52. The term “diameter” of the innerdiameter is generally associated with a circular shape. However, acontour of the inner diameter portion 53 as viewed from a planeperpendicular to the axial line of the shaft member 13 a is not limitedto have a circular shape, and the shape may be, for example, a polygonor an irregular shape.

Welding is performed by bringing the joining end surface 50 of the cupmember 12 a and the joining end surface 51 of the shaft member 13 a intoabutment against each other and irradiating an electron beam from anouter side of the cup member 12 a in the radial direction (FIG. 2a andFIG. 2b ). The welded portion 49, as is well known, comprises metal thatis molten and solidified during welding, that is, a molten metal and aheat-affected portion in a periphery of the molten metal (see FIG. 25band FIG. 26b ).

Although detailed description is made later, outer diameters B of thejoining end surfaces 50 and 51 (see FIG. 4b and FIG. 5c ) are set toequal dimensions for each joint size. However, the outer diameter B ofthe joining end surface 50 of the cup member 12 a and the outer diameterB of the joining end surface 51 of the shaft member 13 a need not be setto equal dimensions. In consideration of, for example, a state of thebead, a dimensional difference may be given as appropriate in such amanner that the outer diameter B of the joining end surface 51 is setslightly smaller than the outer diameter B of the joining end surface 50or the like. The dimensional relationship between the outer diameter Bof the joining end surface 50 and the outer diameter B of the joiningend surface 51 is the same throughout the Description.

The welded portion 49 is formed on the cup member 12 a side with respectto the bearing mounting surface 14 of the shaft member 13 a, and hencethe bearing mounting surface 14 and the like can be processed in advancebefore welding so that post-processing after welding can be omitted.Further, in the electron beam welding, burrs are not generated at thewelded portion. Thus, also on this point, post-processing for the weldedportion can also be omitted, which can reduce manufacturing cost. Stillfurther, total inspection on the welded portion through ultrasonic flawdetection can be performed.

As illustrated in FIG. 2c , an inner diameter D of the joining endsurface 50 of the cup member 12 a is set smaller than an inner diameterE of the inner diameter portion 53 of the joining end surface 51 of theshaft member 13 a. As a result, the joining end surface 50 of the cupmember 12 a partially protrudes to a radially inner side with respect tothe joining end surface 51 having the inner diameter E. This protrudingportion is referred to as a protruding surface 50 a. The joining endsurfaces 50 and 51 having such a shape are brought into abutment againsteach other, and the cup member 12 a and the shaft member 13 a are joinedby welding. The protruding surface 50 a is formed to be the same foreach joint size.

Next, the manufacturing method of the above-mentioned outer joint memberis described with reference to FIG. 3 to FIG. 16. Before description ofdetails of each manufacturing step, an overview of manufacturing stepsis described.

As illustrated in FIG. 3, the cup member 12 a is manufactured throughmanufacturing steps comprising a bar material cutting step S1 c, aforging step S2 c, an ironing step S3 c, and a turning step S4 c.

Meanwhile, the shaft member 13 a is manufactured through manufacturingsteps comprising a bar material cutting step S1 s, a turning step S2 s,and a spline processing step S3 s.

The cup member 12 a and the shaft member 13 a thus manufactured are eachassigned with a product number for management. After that, the cupmember 12 a and the shaft member 13 a are subjected to a welding stepS6, an ultrasonic flaw detection step S6 k, a heat treatment step S7,and a grinding step S8 so that the outer joint member 11 is completed.

An overview of each step is described below. Each step is described as atypical example, and appropriate modification and addition may be madeas needed.

First, the manufacturing steps for the cup member 12 a are described.

[Bar Material Cutting Step S1 c]

A bar material (round bar) is cut into a predetermined length inaccordance with a forging weight, thereby producing a columnar billet.

[Forging Step S2 c]

The billet is subjected to forging so as to integrally form thecylindrical portion, the bottom portion, and the projecting portion as apreform of the cup member 12 a.

[Ironing Step S3 c]

Ironing is performed on the track grooves 30 and the cylindrical surface42 of the preform, thereby finishing the inner periphery of thecylindrical portion of the cup member 12 a.

[Turning Step S4 c]

In the preform after ironing, the outer peripheral surface, the bootmounting groove 32, the snap ring groove 33 and the like, and thejoining end surface 50 are formed by turning. After the turning step S4c, the cup member 12 a in the form of an intermediate component isassigned with a product number for management.

Next, the manufacturing steps for the shaft member 13 a are described.

[Bar Material Cutting Step S1 s]

A bar material is cut into a predetermined length in accordance with anentire length of the shaft section, thereby producing a columnar billet.After that, the billet is forged into a rough shape by upset forgingdepending on the shape of the shaft member 13 a.

[Turning Step S2 s]

The outer peripheral surface of the billet (bearing mounting surface 14,snap ring groove 15, minor diameter of the spline, end surface, and thelike) and the joining end surface 51 of the billet at the end portion onthe cup member 12 a side are formed by turning.

[Spline Processing Step S3 s]

The spline shaft is formed by processing splines in the shaft memberthrough rolling after turning. Note that, the method of processing thespline is not limited to the rolling, and press working or the like maybe adopted instead as appropriate. After the spline processing, theshaft member 13 a in the form of an intermediate component is assignedwith a product number for management.

Next, the manufacturing steps in the process of completing the outerjoint member 11 from the cup member 12 a and the shaft member 13 a inthe form of the intermediate component obtained in the manner describedabove are described.

[Welding Step S6]

The joining end surface 50 of the cup member 12 a and the joining endsurface 51 of the shaft member 13 a are brought into abutment againstand welded to each other. This welding step is described later indetail.

[Ultrasonic Flaw Detection Step S6 k]

The welded portion 49 between the cup member 12 a and the shaft member13 a is inspected by ultrasonic flaw detection. This ultrasonic flawdetection step is also described later in detail.

[Heat Treatment Step S7]

High frequency quenching and tempering are performed as heat treatmenton at least the track grooves 30 and the inner peripheral surface 42 ofthe cup section 12 after welding and a necessary range of the outerperiphery of the shaft member 13 after welding. Heat treatment is notperformed on the welded portion 49. A hardened layer having a hardnessof approximately from 58 HRC to 62 HRC is formed on each of the trackgrooves 30 and the inner peripheral surface 42 of the cup section 12 bythe heat treatment. Further, a hardened layer having a hardness ofapproximately from 50 HRC to 62 HRC is formed in a predetermined rangeof the outer periphery of the shaft section 13.

[Grinding Step S8]

After the heat treatment, the bearing mounting surface 14 of the shaftmember 13 and the like are finished by grinding. Thus, the outer jointmember 11 is completed.

As described above, the heat treatment step is provided after thewelding step, and hence the manufacturing steps are suited to a cupmember and a shaft member having such shapes and specifications that thehardness of the heat-treated portion may be affected by temperature riseat the periphery due to heat generated during the welding.

Main constituent features of the above-mentioned method of manufacturingthe outer joint member are described more in detail.

FIG. 4a is an illustration of a state after ironing of the cup member 12a. FIG. 4b is an illustration of a state after turning. In a preform 12a′ for the cup member 12 a, there are integrally formed a cylindricalportion 12 a 1′, a bottom portion 12 a 2′, and a short shaft section 12a 3′ in the forging step S2 c. After that, the track grooves 30 and thecylindrical surface 42 are formed by ironing in the ironing step S3 c sothat the inner periphery of the cylindrical portion 12 a 1′ is finishedas illustrated in FIG. 4a . After that, in the turning step S4 c, theouter peripheral surface, the boot mounting groove 32, the snap ringgroove 33, and the like of the cup member 12 a as well as the joiningend surface 50 of the short shaft section 12 a 3 and the outer diameterB and the inner diameter D of the joining end surface 50 are formed byturning as illustrated in FIG. 4 b.

FIG. 5a and FIG. 5b are illustrations of states of the shaft member 13 ain the respective processing steps. That is, FIG. 5a is an illustrationof a billet 13 a″ obtained by cutting a bar material. FIG. 5b is anillustration of a preform 13 a′ obtained by forging the billet 13 a″into a rough shape by upset forging. FIG. 5c is an illustration of theshaft member 13 a after turning and spline processing.

The billet 13 a″ illustrated in FIG. 5a is formed in the bar materialcutting step S1 s. The preform 13 a′ is formed by increasing, ifnecessary, the shaft diameter of the billet 13 a″ in a predeterminedrange and forming a recess 52 at a joining-side end portion (end portionon the cup member 12 a side) by upset forging as illustrated in FIG. 5b.

After that, in the turning step S2 s, the outer diameter of the shaftmember 13 a, the bearing mounting surface 14, the snap ring groove 15,an inner diameter portion 53 (inner diameter E), the joining end surface51, and the outer diameter B thereof are formed by turning, asillustrated in FIG. 5c . Further, in the spline processing step S3 s,the spline shaft Sp is processed at the end portion on the opposite sideto the recess 52 by rolling or press forming.

The outer diameter B of the joining end surface 50 of the cup member 12a illustrated in FIG. 4b is set to an equal dimension for one jointsize. Further, in the shaft member 13 a illustrated in FIG. 5c , whichis used for a long stem shaft type, the outer diameter B of the joiningend surface 51 located at the end portion on the cup member 12 a side isset to an equal dimension to the outer diameter B of the joining endsurface 50 of the cup member 12 a irrespective of the shaft diameter andthe outer peripheral shape. Still further, the joining end surface 51 ofthe shaft member 13 a is located at the position on the cup member 12 aside with respect to the bearing mounting surface 14.

Through the setting of dimensions as described above, the outer jointmember 11 compatible with various vehicle types can be manufactured insuch a manner that, while the cup member 12 a is prepared for commonuse, only the shaft member 13 a is manufactured to have a variety ofshaft diameters, lengths, and outer peripheral shapes depending onvehicle types, and both the members 12 a and 13 a are welded to eachother. Details of the preparation of the cup member 12 a for common useare described later.

Next, welding of the cup member 12 a and the shaft member 13 a isdescribed with reference to FIG. 6 and FIG. 7. FIG. 6 is a schematicelevation view of a welding apparatus for illustrating a state beforewelding, and FIG. 7 is a schematic plan view of the welding apparatusfor illustrating a state during welding.

As illustrated in FIG. 6, a welding apparatus 100 mainly comprises anelectron gun 101, a rotation device 102, a chuck 103, a center 104, atailstock 105, workpiece supports 106, a center 107, a case 108, and avacuum pump 109.

The cup member 12 a and the shaft member 13 a being workpieces areplaced on the workpiece supports 106 arranged inside the weldingapparatus 100. The chuck 103 and the centering jig 107 arranged at oneend of the welding apparatus 100 are coupled to the rotation device 102.The chuck 103 grips the cup member 12 a to rotate the cup member 12 a bythe rotation device 102 under a state in which the center 107 hascentered the cup member 12 a. The center 104 is integrally mounted tothe tailstock 105 arranged at another end of the welding apparatus 100.Both the center 104 and the tailstock 105 are configured to reciprocatein the axial direction (lateral direction of FIG. 6).

A center hole of the shaft member 13 a is set on the center 104 so thatthe shaft member 13 a is centered. The vacuum pump 109 is connected tothe case 108 of the welding apparatus 100. A “sealed space” hereinrefers to a space 111 defined by the case 108. The cup member 12 a andthe shaft member 13 a are entirely received in the sealed space 111. Theelectron gun 101 is arranged at a position corresponding to the joiningend surfaces 50 and 51 of the cup member 12 a and the shaft member 13 a.The electron gun 101 is configured to be approachable to and separablefrom the workpieces.

The operation of the welding apparatus 100 constructed as describedabove and the welding method are described below.

The cup member 12 a and the shaft member 13 a being workpieces arestocked at a place different from the place of the welding apparatus100. The respective workpieces are taken out by, for example, a robot,are conveyed into the case 108 of the welding apparatus 100 opened tothe air as illustrated in FIG. 6, and are set at predetermined positionsof the workpiece supports 106. At this time, the center 104 and thetailstock 105 are retreated to the right side of FIG. 6, and hence a gapis formed between the joining end surfaces 50 and 51 of the cup member12 a and the shaft member 13 a.

After that, a door (not shown) of the case 108 is closed, and the vacuumpump 109 is activated to reduce the pressure in the sealed space 111defined in the case 108. Thus, the pressures in the recessed portion 50b of the cup member 12 a and the recessed portions 52 and 53 of theshaft member 13 a are reduced as well.

When the pressure in the sealed space 111 is reduced to a predeterminedpressure, the center 104 and the tailstock 105 are advanced to the leftside as illustrated in FIG. 7 to eliminate the gap between the joiningend surfaces 50 and 51 of the cup member 12 a and the shaft member 13 a.Thus, the cup member 12 a is centered by the center 107 and fixed by thechuck 103, whereas the shaft member 13 a is centered and supported bythe center 104. After that, the workpiece supports 106 are moved awayfrom the workpieces (12 a and 13 a). At this time, the distance betweenthe workpiece supports 106 and the workpieces (12 a and 13 a) may beinfinitesimal, and hence illustration of this distance is omitted fromFIG. 7. As a matter of course, the welding apparatus 100 may have such astructure that the workpiece supports 106 are retreated downwardgreatly.

Although illustration is omitted, the electron gun 101 is then caused toapproach the workpieces (12 a and 13 a) up to a predetermined position,and the workpieces (12 a and 13 a) are rotated to start pre-heating. Asa pre-heating condition, unlike the welding condition, the temperatureis set lower than the welding temperature by, for example, radiating anelectron beam under a state in which the electron gun 101 is caused toapproach the workpieces (12 a and 13 a) so as to increase the spotdiameter. Through the pre-heating, the input heat amount is increased,and with the post-heating described later, the cooling rate at thewelded portion after welding is reduced, thereby being capable ofpreventing a quenching crack.

When a predetermined pre-heating time has elapsed, the electron gun 101is retreated to a predetermined position, and radiates the electron beamfrom the outer side of the workpieces (12 a and 13 a) in the radialdirection to start welding. During one rotation of the workpieces (12 aand 13 a), the welding is performed for the entire periphery, and theannular welded portion 49 is formed.

The post-heating is performed to reduce the cooling rate at the weldedportion 49 and prevent quenching.

When the welding is finished, the electron gun 101 is retreated, and therotation of the workpieces (12 a and 13 a) is stopped.

Although illustration is omitted, the sealed space 111 is then opened tothe air. Then, the center 104 and the tailstock 105 are retreated to theright side in the drawing sheet and the chuck 103 is opened under astate in which the workpiece supports 106 are raised to support theworkpieces. After that, for example, the robot grips the workpieces (12a and 13 a), takes the workpieces out of the welding apparatus 100, andplaces the workpieces into alignment on a cooling stocker. In thisembodiment, the cup member 12 a and the shaft member 13 a are entirelyreceived in the sealed space 111, and hence the configuration of thesealed space 111 defined in the case 108 can be simplified.

Specific conditions for welding are exemplified below.

The cup member 12 a having a carbon content of from 0.4% to 0.6% and theshaft member 13 a having a carbon content of 0.3% to 0.55% were used andwelded to each other in the welding apparatus 100 under the conditionthat the pressure in the sealed space 111 defined in the case 108 wasset to 6.7 Pa or less. In order to prevent rapid cooling after thewelding to suppress excessive increase in hardness of the weldedportion, a periphery including the joining end surfaces 50 and 51 of thecup member 12 a and the shaft member 13 a were soaked by pre-heatingwith the electron beam to have a temperature of from 300° C. to 650° C.,and then electron beam welding was performed. As a result, thepre-heating time was able to be reduced to approximately one-half orless as compared to the case where the recess is not formed in thejoining end surface, and a favorable welded portion satisfying therequired strength was able to be obtained.

As a result, a welded portion having a projecting height from the weldedsurface (0.5 mm or less), which imposed no adverse effect on a productfunction, was obtained. Further, through the soaking by pre-heating, thehardness of the welded portion after completion of the welding was ableto be kept within a range of from 200 HV to 500 HV, thereby beingcapable of attaining high welding strength and stable welding state andquality. Still further, welding was performed under the condition thatthe pressure in the sealed space 111 defined in the case 108 of thewelding apparatus 100 was set to 6.7 Pa or less, thereby being capableof suppressing the change in pressure in the recess 52 and the recessedportion 50 b during the welding. As a result, the blowing of a moltenmaterial and the entry of the molten material toward the radially innerside were able to be prevented.

Next, features of the outer joint member of the embodiment and themethod of manufacturing the outer joint member are described withreference to FIG. 23 and FIG. 24, and then the findings obtained as aresult of verification in the course of development is described asComparative Example with reference to FIG. 25 and FIG. 26. FIG. 23 andFIG. 25 are associated with each other. FIG. 23 shows a heat history ofExample, and FIG. 25 shows a heat history of Comparative Example. FIG.24 and FIG. 26 are also associated with each other. FIG. 24 is amicrophotograph showing the structure of the welded portion of Example.FIG. 26 is a microphotograph showing the structure of the welded portionof Comparative Example.

In FIG. 23, the horizontal axis represents time (s), and the verticalaxis represents temperature (° C.). The pre-heating was performed over15.2 s to about 200° C. The welding required 6.2 s, and during thewelding, the temperature has risen to a melting point of steel (about1,600° C.) or higher. After the welding, air-cooling was performed. Fromthe time point of 33.8 s later and below about 530° C., the post-heatingis started to perform heating over 15.2 s to about 600° C. After that,air-cooling was performed. In order to avoid formation of themartensite, the temperature rise by the post-heating was less than atransformation point A₁ (723° C.).

The structure of the welded portion at a normal temperature is, asillustrated in FIG. 24a , in a mixed phase of ferrite and cementite. Thebase portion is ferrite, and granular cementite is precipitated. Thehardness was from 280 HV to 380 HV. FIG. 24a is an opticalmicrophotograph showing a portion surrounded by a rectangle at a centerof the welded portion as illustrated in FIG. 24b . As is well known, themicrophotograph was taken in the following manner. A test piece wascutout from the workpiece. An observation surface was mirror-polishedand washed with water. After that, an etchant for revealing thestructure was used (picral (picric acid solution) was used) to causecorrosion in the observation surface, and the observation surface waswashed with water again. Then, the microphotograph of the observationsurface was taken with an optical microscope. This holds true also forthe case of the Comparative Example described later.

Also in FIG. 25 for showing the heat history of the Comparative Example,the horizontal axis represents time (s), and the vertical axisrepresents temperature (° C.). The pre-heating was performed over 84 sto about 600° C. The welding required 6.2 s as in Example describedabove, and during the welding, the temperature has risen to the meltingpoint of steel (about 1, 600° C.) or higher. After the welding,air-cooling was performed without performing the post-heating. Thestructure of the welded portion at a normal temperature is, asillustrated in FIG. 26a , in a mixed phase of pearlite and stripeferrite, and the hardness was from 280 HV to 310 HV. FIG. 26a is anoptical microphotograph showing a portion surrounded by a rectangle at acenter of the welded portion as illustrated in FIG. 26b . In FIG. 24band FIG. 26b , the welded portion 49 includes the molten metal denotedby the reference symbol 49 a, and the heat-affected portion denoted bythe reference symbol 49 b.

A total of 90.2 s was required for pre-heating and welding inComparative Example, whereas a total of 36.4 s was required forpre-heating, welding, and post-heating. Thus, the welding cycle time wasreduced by 58.8 s. In the case of Comparative Example, in order toprevent the cooling rate causing the transformation into the martensitethrough rapid cooling after the welding, it is necessary to sufficientlyincrease the input heat amount through pre-heating. Thus, thetemperature was raised to about 600° C. through pre-heating for 84 s. Onthe other hand, in the case of Example, the temperature was raised toabout 600° C. through post-heating for 15.2 s after the welding. Theinput heat by welding can be utilized in the post-heating, and hence thetime may be short, and the pre-heating time of about one-sixth ascompared to the Comparative Example was sufficient.

The electron gun 101 for welding can be utilized for the pre-heating andpost-heating. In that case, the input heat amount can be adjusted byincreasing or decreasing the spot diameter of the electron beam.Alternatively, another electron gun other than the electron gun 101 forwelding may be provided. That is, two or more electron guns may beprovided. In that case, for example, the electron guns may be arrangedwith a predetermined distance in the circumferential direction, that is,the rotation direction of the workpieces to be used for pre-heating,welding, and post-heating. The increase in cost is inevitable, but sucha configuration is advantageous in terms of reducing the cycle time.

Next, the ultrasonic flaw detection step is described with reference toFIG. 8 to FIG. 13.

Herein, FIG. 8 and FIG. 9 are a front view and a plan view,respectively, of an ultrasonic flaw-detection apparatus having a weldedouter joint member mounted thereto. FIG. 8 corresponds to anillustration as viewed from the direction of the arrow VIII-VIII of FIG.9. FIG. 10 and FIG. 11 are a front view and a plan view, respectively,of the ultrasonic flaw-detection apparatus during the ultrasonic flawdetection. FIG. 10 corresponds to an illustration as viewed from thedirection of the arrow X-X of FIG. 11.

As illustrated in FIG. 8 and FIG. 9, an ultrasonic flaw-detectionapparatus 120 mainly comprises a base 121, a water bath 122, a workpiecesupport 123, a workpiece holding member 124, a rotary drive device 125,a pressing device 135, and a drive positioning device 136 (see FIG. 9).The water bath 122 is mounted at the center of the base 121. The rotarydrive device 125 is configured to rotate an intermediate product 11′(hereinafter also referred to as “workpiece 11′”) of the outer jointmember 11. The pressing device 135 is configured to press an axial endof the workpiece 11′. The drive positioning device 136 is configured todrive and position a probe.

The workpiece support 123 comprises support rollers 126 and 127configured to allow the workpiece 11′ to be placed thereon in a freelyrotatable manner. The support rollers 126 are arranged at a positionclose to the welded portion. The support rollers 127 are arranged near acenter portion of the shaft section 13. As is apparent from FIG. 9, thesupport rollers 126 and 127 are constructed by pairs of rollers providedon both sides in the axial line of the shaft section 13 so that theshaft section 13 of the workpiece 11′ can be stably supported. Thesupport rollers 126 and 127 are capable of adjusting the placementposition of the workpiece 11′ in the axial direction (lateral directionof FIG. 8) and the radial direction (vertical direction of FIG. 8) inconsideration of a joint size, dimensions, and weight balance of theworkpiece 11′.

Further, the workpiece holding member 124 is mounted to the workpiecesupport 123 at a position displaced in a plane of FIG. 9 from an axialline of the workpiece 11′. The workpiece holding member 124 comprises alever 128, and a workpiece holding roller 129 is arranged at an endportion of the lever 128. The lever 128 is pivotable in the plane ofFIG. 9, and is movable in the vertical direction of FIG. 8.

The workpiece support 123 is mounted to a support 134 throughintermediation of a linear-motion bearing 130 comprising rails 131 andlinear guides 132, and is movable in the axial direction (lateraldirection of FIG. 8 and FIG. 9). The support 134 is mounted to the base121. The workpiece support 123 can be driven to be positioned at adesired position by an actuator (not shown) arranged on an outside ofthe water bath 122 through intermediation of a rod 133 coupled to an endportion (left end portion of FIG. 8 and FIG. 9).

The rotary drive device 125 comprises a rotary shaft 143 having a rotarydisc 144 mounted thereto, and this rotary shaft 143 is driven to rotateby a motor (not shown) arranged on the outside of the water bath 122.

A mounting base 137 is arranged on an upper side of the ultrasonicflaw-detection apparatus 120. A base plate 145 for the pressing device135 is mounted to the mounting base 137 through intermediation of alinear-motion bearing 138 comprising a rail 139 and a linear guide 140so that the base plate 145 of the pressing device 135 is movable in theaxial direction (lateral direction of FIG. 8 and FIG. 9). A rod 142 of apneumatic cylinder 141 is coupled to an end portion of the base plate145 so that the base plate 145 is driven, that is, axially moved by thepneumatic cylinder 141. The pressing device 135 is held in abutmentagainst the axial end of the shaft section 13 of the workpiece 11′through a free bearing 146.

As viewed in the plane of FIG. 9, the drive device 136 for a probe isarranged at a position displaced in the axial line of the workpiece 11′.This drive device 136 comprises actuators for the X-axis direction andthe Y-axis direction so that a probe 147 is driven to be positioned inthe X-axis direction and the Y-axis direction. An actuator 148 for theX-axis direction and an actuator 149 for the Y-axis direction are eachan electric ball-screw type (ROBO cylinder), which is capable ofperforming positioning with high accuracy. The reference symbol 150denotes a rail for a linear-motion bearing. The drive device 136 isarranged on the outside of the water bath 122, and the probe 147 and aholder 151 therefor are arranged in the water bath 122.

Next, the operation of the ultrasonic flaw-detection apparatus 120having the above-mentioned configuration and the ultrasonic flawdetection step S6 k are described below.

First, the workpiece 11′ after welding is placed on the workpiecesupport 123 by a loader (not shown) (see FIG. 8 and FIG. 9). At thistime, the workpiece support 123 is located at an appropriate intervalfrom the rotary drive device 125 in the axial direction of the workpiece11′, and the workpiece holding member 124 raises and pivots the lever128 thereof so as to be substantially parallel to the axial line of theworkpiece 11′. Further, the pressing device 135 and the drive device 136for a probe wait at retreated positions.

After that, the lever 128 of the workpiece holding member 124 is pivotedso as to be substantially perpendicular to the axial line of theworkpiece 11′, and then lowered to hold the workpiece 11′ from above(see FIG. 10). Then, water is supplied to the water bath 122. Asdescribed above, the ultrasonic flaw-detection apparatus 120 has theconfiguration of performing flaw detection under water, and henceultrasonic waves are satisfactorily propagated. Thus, inspection can beperformed with high accuracy.

Next, as illustrated in FIG. 10 and FIG. 11, the pneumatic cylinder 141is driven to cause the pressing device 135 to be advanced and pressedagainst the axial end of the workpiece 11′, thereby pressing the openingrim of the cup section 12 of the workpiece 11′ against the rotary disc144 of the rotary drive device 125. In conjunction with the advance ofthe pressing device 135, the workpiece support 123 is also moved towardthe rotary drive device 125. Thus, the workpiece 11′ is positioned inthe axial direction and the radial direction. In this state, the motor(not shown) of the rotary drive device 125 is activated, therebyrotating the workpiece 11′.

As illustrated in FIG. 11 with the outlined arrow, the drive device 136is moved in the X-axis direction, and then moved in the Y-axisdirection, thereby positioning the probe 147 at a flaw detectionposition. The probe 147 in this state is indicated by the broken line inFIG. 10. Then, the ultrasonic flaw detection is performed. After thecompletion of the ultrasonic flaw detection, water is drained from thewater bath 122, and the workpiece 11′ is delivered from the ultrasonicflaw-detection apparatus 120 by the loader (not shown). In such amanner, the ultrasonic flaw detection is sequentially repeated on theworkpiece 11′.

In order to reduce the cycle time of the ultrasonic flaw detection, itis desired that time-consuming supply and drainage of water be performedsimultaneously with operations of the devices and the members, or atother timings in accordance therewith. Further, some of the operationsof the devices and the members may be performed simultaneously with eachother or in different orders as appropriate.

Details of the ultrasonic flaw detection are described with reference toFIG. 12a , FIG. 12b , and FIG. 13. All of FIG. 12a , FIG. 12b , and FIG.13 are views as viewed from the arrow XII-XII of FIG. 10. FIG. 12a is anillustration of a non-defective welded product. FIG. 12b is anillustration of a defective welded product. FIG. 13 is a view forillustrating findings in the course of development.

The probe 147 is positioned at a flaw detection position away from thewelded portion 49 by a predetermined distance. The flaw detectionposition is preset for each joint size. A transmission pulse G from theprobe 147 is caused to obliquely enter from a surface of the workpiece11′. A reflected echo having been received is displayed as waveforms,and the waveforms may be observed to determine a presence or absence ofdefectiveness (angle beam flaw detection method). The reference symbolθ1 denotes an incident angle, and the reference symbol θ2 denotes arefraction angle. In the case of the embodiment, the incident angle θ1is about 20°, and the refraction angle θ2 is about 45°.

Herein, a presence or absence of the penetration defectiveness is mainlydetected through detection of a position of a back bead. That is,workpieces having a penetration depth equal to or larger than adetermination reference Wmin to reach a radially inner side aredetermined as non-defective welded products, and workpieces having apenetration depth smaller than the determination reference Wmin toterminate on a radially outer side are determined as defective weldedproducts. In the illustrated example, the inner diameter portion 53 ofthe recess 52 formed in the joining end surface 51 is matched with thedetermination reference Wmin. The reference symbol E denotes an innerdiameter of (the inner diameter portion 53 of) the recess 52, and alsodenotes an inner diameter of the joining end surface 51. The referencesymbol Wa denotes a target penetration depth. Incidentally, after thewelding, the welded portion 49 is formed on the radially outer side ofthe recess 52. As a result, a closed cavity is formed on the radiallyinner side of the welded portion 49. Thus, a back bead 491 cannot bevisually confirmed from outside.

During the ultrasonic flaw detection, the workpiece 11′ is driven by therotary drive device 125 to rotate. The probe 147 positioned at the flawdetection position away from the welded portion 49 by the predetermineddistance collects data of the entire periphery of the workpiece 11′. Inconsideration of tolerance for displacement of the welding position, atthe above-mentioned flaw detection position, first, data of a singlerotation (360°) of the workpiece 11′ is collected. Then, the probe 147is sequentially shifted in the axial direction at a minute pitch (forexample, 0.5 mm) to collect data of a plurality of rotations (forexample, five rotations). Based on those pieces of data,non-defective/defective determination is made. A threshold of areflected echo to be used in the non-defective/defective determinationis determined based on a welding pattern corresponding to thedetermination reference Wmin.

As already described above, in the joining end surface 50 of the cupmember 12 a, there is formed the protruding surface 50 a which protrudestoward the radially inner side with respect to the inner diameter E ofthe joining end surface 51 of the shaft member 13 a. With theabove-mentioned shape, the following advantages in the ultrasonic flawdetection can be obtained.

For easy understanding of the above-mentioned advantages, description ispreferentially made of findings in the course of development, that is,the case in which an inner diameter D′ of the joining end surface 50 ofthe cup member 12 a is set to an equal dimension to the inner diameter Eof the joining end surface 51 of the shaft member 13 a as illustrated inFIG. 13. In this case, the penetration depth is equal to or larger thanthe determination reference Wmin to reach the radially inner side, andhence the workpiece is to be determined as a non-defective weldedproduct. However, when the transmission pulse G enters from the probe147, due to the boundary surface of the back bead 491, which isperpendicular to the transmission pulse G, a reflected echo R reflectedby this boundary surface is received by the probe 147. Althoughreflected echoes from the back bead 491 are scattered, the reflectedecho R has a large echo height exceeding the threshold of the reflectedecho for the non-defective/defective determination. Thus, determinationthat the welded product is defective is made. For this reason, it wasproved that the determination as to whether the welded product wasnon-defective or defective was difficult.

Thus, in the embodiment, a measure is taken by forming the protrudingsurface 50 a, which protrudes toward the radially inner side withrespect to the inner diameter E of the joining end surface 51 of theshaft member 13 a, in the joining end surface 50 of the cup member 12 a.

As illustrated in FIG. 12a , the non-defective welded product hassufficient penetration. In this case, the transmission pulse G from theprobe 147 enters the cup section 12 through the back bead 491 havingreached the radially inner side beyond the determination reference Wmin,and travels straight as it is. Alternatively, the transmission pulse Gtravels to the cup section 12 side by being reflected due to the innerdiameter D of the cup section 12. Therefore, the probe 147 does notreceive a reflected echo. That is, even when the transmission pulse Genters the back bead 491, the boundary surface of the back bead 491,which is perpendicular to the transmission pulse G, does not exist.Therefore, although a slightly-scattered reflected echo is generated,the reflected echo which may cause the detection error is not generated.Thus, the echo height of the reflected echo received by the probe 147 isequal to or less than the threshold, and hence determination that thewelded product is non-defective is made.

As described above, when the protruding surface 50 a is formed on thejoining end surface 50 of the cup member 12 a, the echo height of thereflected echo becomes lower. Thus, the accuracy in the inspection canbe enhanced.

In the case of the defective welded product, as illustrated in FIG. 12b, a distal end of the bead 491 does not reach the determinationreference Wmin due to the defective penetration. Thus, the transmissionpulse G is reflected by the joining end surface 51 and a chamferedportion 51 a, and the scattered reflected echo R is received by theprobe 147. The reflected echo R exceeds the threshold of the reflectedecho for the non-defective/defective determination, and hencedetermination that the welded product is defective is made.

As described above, the protruding surface 50 a is formed on the joiningend surface 50, and hence the echo heights of the reflected echoes canbe clearly discriminated from each other. Thus, the determination as towhether the welded product is non-defective or defective can be madewith high accuracy.

Dimensions of the protruding surface 50 a are set so that a relationshipof S≥Q is established, where S [S=(E−D)/2] is a width of the protrudingsurface 50 a in a radial direction, and where Q is a height of the backbead 491 from the inner diameter E of the joining end surface 51 asillustrated in FIG. 12a . When this relationship is satisfied, theheights of the reflected echoes can be clearly discriminated from eachother. Thus, the determination as to whether the welded product isnon-defective or defective can be made with high accuracy. As long asthe relationship of S≥Q is maintained, the dimensions of the protrudingsurface 50 a may be set as appropriate. The inner diameter E of thejoining end surface 51 is also an inner diameter (of the inner diameterportion 53) of the recess 52.

In the ultrasonic flaw-detection apparatus 120, the operation of loadingthe workpiece 11′, the supply and drainage of water, the ultrasonic flawdetection, and the operation of unloading the workpiece can be performedin conjunction with each other, and the ultrasonic flaw detection can beautomated. Thus, accuracy, operability, and efficiency in the inspectioncan be enhanced, which is suited to the inspection on the welded portionof the outer joint member of the constant velocity universal joint beinga mass-produced product.

Further, in the ultrasonic flaw detection, with the base configurationin which the outer diameter B of the joining end surface 50 of the cupmember 12 a is set to an equal dimension for each joint size, setup andreplacement operations with respect to the outer joint members 11 havingthe different product numbers are reduced. Thus, the efficiency in theinspection can be further enhanced.

Still further, flaw detection is performed under water, and henceultrasonic waves are satisfactorily propagated. Thus, inspection can beperformed with much higher accuracy. In addition, through employment ofthe shape of the welded portion, in which the protruding surface 50 a isformed on the joining end surface 50, the echo heights of the reflectedechoes can clearly be discriminated from each other. Thus, thedetermination as to whether the welded product is non-defective ordefective can be made with high accuracy.

Next, standardization of a product type of the cup member isadditionally described while exemplifying a shaft member having aproduct number different from that of the above-mentioned shaft member13 a of the long stem type illustrated in FIG. 5 c.

A shaft member 13 b illustrated in FIG. 14 and FIG. 15 is used as ageneral stem type on the inboard side. The shaft member 13 b has thejoining end surface 51 to be brought into abutment against the joiningend surface 50 (see FIG. 4b ) of the bottom portion 12 a 2 (short shaftsection 12 a 3) of the cup member 12 a. The outer diameter B and theinner diameter E of the joining end surface 51 are set to the equaldimensions to the outer diameter B and the inner diameter E of thejoining end surface 51 of the shaft member 13 a of the long stem typeillustrated in FIG. 5 c.

Also in this case, the inner diameter D of the joining end surface 50 ofthe cup member 12 a is set smaller than the inner diameter E of thejoining end surface 51 of the shaft member 13 b. As a result, on thejoining end surface 50 of the cup member 12 a, the protruding surface 50a protruding to the radially inner side with respect to the innerdiameter E of the joining end surface 51 of the shaft member 13 b isformed. The joining end surfaces 50 and 51 having such shape are broughtinto abutment against each other to be welded so that the cup member 12a and the shaft member 13 b are joined to each other.

The shaft member 13 b is used as the general stem type on the inboardside. Accordingly, the shaft member 13 b comprises a shaft section witha small length, and a sliding bearing surface 25 formed on an axialcenter portion thereof, and a plurality of oil grooves 26 are formed inthe sliding bearing surface 25. The spline shaft Sp and the snap ringgroove 48 are formed in an end portion on the side opposite to the cupmember 12 a side. As described above, even when there are differences intypes, such as the general length stem type and the long stem type, andshaft diameters and outer peripheral shapes vary in each vehicle type,the outer diameter B of the joining end surface 51 of the shaft member13 a or 13 b is set to an equal dimension.

The outer diameter B of the joining end surface 50 of the cup member 12a and the joining end surface 51 of the shaft member 13 a or 13 b is setto an equal dimension for each joint size. Thus, the cup member preparedfor common use for each joint size, and the shaft member having avariety of specifications of the shaft section for each vehicle type canbe prepared in a state before heat treatment. Further, the intermediatecomponent of each of the cup member 12 a and the shaft member 13 a or 13b can be assigned with a product number for management. Even whenstandardizing product types of the cup member 12 a, various types of theouter joint members satisfying requirements can be produced quicklythrough combination of the cup member 12 a and the shaft member 13 a or13 b having a variety of specifications of the shaft section for eachvehicle type. Therefore, standardization of a product type of the cupmember 12 a can reduce cost and alleviate a burden of productionmanagement.

The standardization of the product type of the cup member is describedabove by taking the differences in types, such as the general lengthstem type and the long stem type, as an example for easy understanding,but the present invention is not limited thereto. The same applies tostandardization of the product type of the cup member for shaft membershaving a variety of specifications of the shaft section for each vehicletype among the general length stem types, and for shaft members having avariety of specifications of the shaft section for each vehicle typeamong the long stem types.

An example of standardization of a product type of the cup member isillustrated in FIG. 16.

As illustrated in FIG. 16, the cup member is prepared for common use forone joint size, and is assigned with, for example, a product number C001for management. In contrast, the shaft member has a variety ofspecifications of the shaft section for each vehicle type, and isassigned with, for example, a product number S001, S002, or S(n) formanagement. For example, when the cup member assigned with the productnumber C001 and the shaft member assigned with the product number S001are combined and welded to each other, the outer joint member assignedwith a product number A001 can be produced.

Thus, owing to standardization of a product type of the cup member, itis possible to reduce cost and to alleviate a burden of productionmanagement. In the standardization of a product type, the cup member isnot limited to one type for one joint size, that is, not limited to onetype assigned with a single product number. For example, the cup membercomprises cup members of a plurality of types (assigned with a pluralityof product numbers, respectively) that are prepared for one joint sizebased on different specifications of a maximum operating angle, and areeach prepared so that the outer diameter B of the joining end surface ofeach of those cup members has an equal dimension.

Next, a second embodiment of the outer joint member is described withreference to FIG. 17a to FIG. 17c and FIG. 18.

FIG. 17a is a partial sectional front view of the outer joint member.FIG. 17b is an enlarged view of a portion “b” of FIG. 17a . FIG. 17c isa view for illustrating a state before welding in FIG. 17b . FIG. 18 isa vertical sectional view for illustrating the cup member beforewelding.

A form of a protruding surface formed on a joining end surface of thecup member of this second embodiment is different from that in the firstembodiment described above. Other configurations are the same as thosein the first embodiment. Thus, parts that have the same function asthose of the first embodiment are denoted by the same reference symbolsexcept for the subscripts, and overlapping description is omitted.

As illustrated in FIG. 17c and FIG. 18, a joining end surface 50 ₁formed on a short shaft section 12 a 3 ₁ of a cup member 12 a ₁ isannular, and a projecting portion 50 b ₁ is formed on the radially innerside. In this case, a diameter D₁ of the annular joining end surface 50₁ on the radially inner side corresponds to the inner diameter D of thejoining end surface 50 of the cup member 12 a of the first embodiment ofthe outer joint member. A portion of the joining end surface 50 ₁ on theradially inner side protrudes toward the radially inner side withrespect to the inner diameter E of the joining end surface 51 of theshaft member 13 a. This protruding portion is referred to as aprotruding surface 50 a ₁ as in the first embodiment.

The cup member 12 a ₁ can be formed by turning an end surface of theshort shaft section 12 a 3′ of the preform 12 a′ (FIG. 4a ) for the cupmember of the first embodiment after ironing at only a portion of thejoining end surface 50 ₁ on the radially outer side. Thus, the time forthe turning can be reduced, with good material yield. As a matter ofcourse, the projecting portion 50 b ₁ on the radially inner side canalso be subjected to turning. However, the number of steps can bereduced by maintaining the forged surface as it is.

Other configurations and operations, that is, the overview of therespective steps, the states of the cup member and the shaft member inthe main processing steps, the preparation of the cup member for commonuse, the welding method, the ultrasonic flaw detection, thestandardization of the product type, the configuration of the outerjoint member, and the like as described above in relation to the firstembodiment of the outer joint member are also applicable to the secondembodiment of the outer joint member.

FIG. 19 is an illustration of a second embodiment of a manufacturingmethod of the outer joint member.

In the second embodiment, the heat treatment step for the cup member,which is involved in the heat treatment step S7 in FIG. 3, is providedbefore the welding step S6 and named “heat treatment step S5 c”, tothereby prepare the cup member as a finished product. Other than thispoint, the matters described above in relation to the first embodimentof the manufacturing method, that is, the overview of the respectivesteps, the states of the cup member and the shaft member in the mainprocessing steps, the preparation of the cup member for common use, thewelding method, the ultrasonic flaw detection, the standardization ofthe product type, the configuration of the outer joint member, and thelike are also applicable to the second embodiment.

As illustrated in FIG. 4b , the cup member 12 a has a shape extendingfrom the joining end surface 50 to the large-diameter cylindricalportion 12 a 1 via the bottom portion 12 a 2, and the portions to besubjected to heat treatment that involves quenching and tempering arethe track grooves 30 and the cylindrical inner peripheral surface 42located at the inner periphery of the cylindrical portion 12 a 1.Therefore, the cup member 12 a generally has no risk of thermal effecton the heat-treated portion during the welding. For this reason, the cupmember 12 a is subjected to heat treatment before the welding to beprepared as a finished product. Such manufacturing steps are suitable inpractical use.

The cup member 12 a is subjected to heat treatment for preparing the cupmember 12 a as a finished product, and is therefore assigned with aproduct number indicating a finished product for management. Thus, thestandardization of the product type of the cup member 12 a remarkablyreduces the cost and alleviates the burden of production management.Further, the cup member 12 a can be manufactured solely until the cupmember 12 a is completed as a finished product through the forging,turning, and heat treatment. Thus, the productivity is enhanced byvirtue of reduction of setups and the like as well.

With regard to FIG. 16 for illustrating the example of standardizationof the product type of the cup member described above in relation to thefirst embodiment of the manufacturing method, only the product number ofthe cup member in FIG. 16 is changed to the product number indicating afinished product, whereas the product numbers of the shaft member andthe outer joint member are the same as those of the first embodiment ofthe manufacturing method. Therefore, description thereof is omittedherein.

FIG. 20 is an illustration of a third embodiment of a manufacturingmethod of the outer joint member.

In the third embodiment, the heat treatment steps for the cup sectionand the shaft section, which are involved in the heat treatment step S7in FIG. 3 described above in relation to the first embodiment, and thegrinding step S8 for the shaft section in FIG. 3 are provided before thewelding step S6 in the sequence and named “heat treatment step S5 c forcup member”, “heat treatment step S4 s for shaft member”, and “grindingstep S5 s”. Thus, both the cup member and the shaft member are preparedas finished products. Other matters, that is, the overview of therespective steps, the states of the cup member and the shaft member inthe main processing steps, the preparation of the cup member for commonuse, the welding method, the ultrasonic flaw detection, thestandardization of the product type, the configuration of the outerjoint member, and the like described in relation to the first embodimentare also applicable to the third embodiment.

After the spline processing step S3 s, a hardened layer having ahardness of approximately from 50 HRC to 62 HRC is formed in apredetermined range of the outer peripheral surface of the shaft memberby induction quenching in the heat treatment step S4 s. Heat treatmentis not performed on a predetermined portion in the axial direction,which includes the joining end surface 51. The heat treatment for thecup member, the assignment of the product number, and the like are thesame as those of the second embodiment on the manufacturing method, andredundant description is therefore omitted herein.

After the heat treatment step S4 s, the shaft member is transferred tothe grinding step S5 s so that the bearing mounting surface 14 and thelike are finished. Thus, the shaft member is obtained as a finishedproduct. Then, the shaft member is assigned with a product numberindicating a finished product for management. The manufacturing steps ofthe third embodiment are suitable in a case of a cup member and a shaftmember having shapes and specifications with no risk of thermal effecton the heat-treated portion during the welding.

In the manufacturing steps of the third embodiment, both the cup memberand the shaft member can be assigned with product numbers indicatingfinished products for management. Thus, the standardization of theproduct type of the cup member further remarkably reduces the cost andalleviates the burden of production management. Further, the cup memberand the shaft member can be manufactured independently of each otheruntil the cup member and the shaft member are completed as finishedproducts through the forging, turning, heat treatment, grinding afterheat treatment, and the like. Thus, the productivity is further enhancedby virtue of reduction of setups and the like as well.

In the case of the third embodiment of the manufacturing method, withregard to FIG. 16 for illustrating the example of standardization of theproduct type of the cup member described above in relation to the firstembodiment, the product numbers of the cup member and the shaft memberin FIG. 16 are changed to the product numbers indicating finishedproducts. The outer joint member is the same as that of the firstembodiment of the manufacturing method. Therefore, description thereofis omitted herein. Note that, the cup member and the shaft member to beprepared as finished products are not limited to the cup member and theshaft member subjected to finishing such as the above-mentioned grindingafter heat treatment or cutting after quenching, and encompass a cupmember and a shaft member in a state in which the heat treatment iscompleted while the finishing is uncompleted.

As described with regard to the standardization of the product type, thecup member is not limited to one type for one joint size, that is, notlimited to one type assigned with a single product number. The cupmember encompasses, for example, cup members of a plurality of types(assigned with a plurality of product numbers, respectively) that areprepared for one joint size based on different specifications of amaximum operating angle, and are also prepared so that the outerdiameters B of the above-mentioned joining end surfaces of the cupmembers are set to equal dimensions. In addition, the cup memberencompasses, for example, cup members of a plurality of types (assignedwith a plurality of product numbers, respectively) that are prepared forone joint size in order to achieve management of the cup members in aplurality of forms including intermediate components before heattreatment and finished components in consideration of the jointfunction, the circumstances at the manufacturing site, the productivity,and the like, and are also prepared so that the outer diameters B of theabove-mentioned joining end surfaces of the cup members are set to equaldimensions.

Next, a third embodiment of the outer joint member is described withreference to FIG. 21 and FIG. 22.

Herein, parts that have the same function as those of the firstembodiment of the outer joint member are denoted by the same referencesymbols, and only main points are described.

A plunging type constant velocity universal joint 10 ₂ illustrated inFIG. 21 is a tripod type constant velocity universal joint (TJ), andcomprises an outer joint member 11 ₂, an inner joint member 16 ₂, androllers 19 serving as torque transmitting elements. The outer jointmember 11 ₂ comprises a cup section 12 ₂ and the long stem section 13that extends from a bottom of the cup section 12 ₂ in the axialdirection. The inner joint member 16 ₂ comprises a tripod member 17comprising three equiangular leg shafts 18 configured to support therollers 19 in a freely rotatable manner, and is housed along an innerperiphery of the cup section 12 ₂ of the outer joint member 11 ₂. Therollers 19 are arranged between the outer joint member 11 ₂ and theinner joint member 16 ₂, and configured to transmit torque therebetween.

Similarly to the first embodiment of the outer joint member, the innerring of the support bearing 6 is fixed to the outer peripheral surfaceof the long stem section 13, and the outer ring of the support bearing 6is fixed to the transmission case with the bracket (not shown). Theouter joint member 11 ₂ is supported by the support bearing 6 in afreely rotatable manner, and thus the vibration of the outer jointmember 11 ₂ during driving or the like is prevented as much as possible.

As illustrated in FIG. 22, the outer joint member 11 ₂ comprises a cupsection 12 ₂ and the long stem section 13. The cup section 12 ₂ has abottomed cylindrical shape that is opened at one end, and has trackgrooves 30 ₂, on which the rollers 19 are caused to roll, formed atthree equiangular positions on an inner peripheral surface 31 ₂. Thelong stem section 13 extends from the bottom of the cup section 12 ₂ inthe axial direction and comprises the spline shaft Sp serving as thetorque transmitting coupling portion formed at the outer periphery ofthe end portion on the side opposite to the cup section 12 ₂.

The outer joint member 11 ₂ is formed by welding the cup member 12 a ₂serving as the cup section 12 ₂ and the shaft member 13 a serving as thelong stem section 13 to each other.

The cup member 12 a ₂ is an integrally-formed product having acylindrical portion 12 a 1 ₂ and a bottom portion 12 a 2 ₂, and hastrack grooves 130 and an inner peripheral surface 131 formed at theinner periphery of the cylindrical portion 12 a 1 ₂. A short shaftsection 12 a 3 ₂ is formed at the bottom portion 12 a 2 ₂. A bootmounting groove 32 is formed at an outer periphery of the cup member 12a ₂ on the opening side.

In the shaft member 13 a, the bearing mounting surface 14 and the snapring groove 15 are formed at the outer periphery on the cup member 12 a₂ side, and the spline shaft Sp is formed at an end portion on the sideopposite to the cup member 12 a ₂.

A joining end surface 50 ₂ formed at the short shaft section 12 a 3 ₂ ofthe cup member 12 a ₂ and the joining end surface 51 formed at the endportion of the shaft member 13 a on the cup member 12 a ₂ side arebrought into abutment against each other, and are welded to each otherby radiating an electron beam from the radially outer side. As is wellknown, the welded portion 49 comprises metal that is molten andsolidified during welding, that is, the molten metal, and theheat-affected portion in the periphery thereof.

Similarly to the first embodiment of the outer joint member, the outerdiameters B of the joining end surface 50 ₂ and the joining end surface51 are set to equal dimensions for each joint size. The welded portion49 is formed on the cup member 12 a ₂ side with respect to the bearingmounting surface 14 of the shaft member 13 a, and hence the bearingmounting surface 14 and the like can be processed in advance so thatpost-processing after welding can be omitted. Further, due to theelectron beam welding, burrs are not generated at the welded portion.Thus, post-processing for the welded portion can also be omitted, whichcan reduce the manufacturing cost.

The matters described in relation to the first and second embodiments ofthe outer joint member and the first to third embodiments of themanufacturing method are also applicable to the third embodiment of theouter joint member.

Herein, with regard to setting of the outer diameters B of the joiningend surface 50, 50 ₁, or 50 ₂ of the cup member 12 a, 12 a ₁, or 12 a ₂and the protruding surfaces 50 a and 50 a ₁ to the equal dimension foreach joint size, the cup member 12 a, 12 a ₁, or 12 a ₂ is not limitedto one type for one joint size, that is, not limited to one typeassigned with a single product number.

For example, the cup member encompasses cup members of a plurality oftypes (assigned with a plurality of product numbers, respectively) thatare prepared for one joint size based on different specifications of amaximum operating angle, and are also prepared so that the outerdiameters of the above-mentioned joining end surfaces of the cup membersare set to equal dimensions and that the protruding surfaces are formedinto the same shape.

In addition, the cup member encompasses, for example, cup members of aplurality of types (assigned with a plurality of product numbers,respectively) that are prepared for one joint size in order to achievemanagement of the cup members in a plurality of forms includingintermediate components before heat treatment and finished components inconsideration of the joint function, the circumstances at themanufacturing site, the productivity, and the like, and are alsoprepared so that the outer diameters of the above-mentioned joining endsurfaces of the cup members are set to equal dimensions and that theprotruding surfaces are formed into the same shape.

Further, setting the outer diameter B of the joining end surface 50, 50₁, or 50 ₂ of the cup member 12 a, 12 a ₁, or 12 a ₂ to an equaldimension for each joint size, or forming the protruding surfaces 50 aand 50 a ₁ into the same shape for each joint size may be applied alsoto different types of constant velocity universal joints.

For example, setting outer diameters of the joining end surfaces of atripod type constant velocity universal joint and a double-offsetconstant velocity universal joint to equal dimensions, and forming theprotruding surface into the same shape on the inboard side are alsoencompassed. Further, setting outer diameters of the joining endsurfaces of a Rzeppa type constant velocity universal joint and anundercut-free constant velocity universal joint to equal dimensions, andforming the protruding surface into the same shape on the outboard sideare also encompassed. Further, setting the outer diameters of thejoining end surfaces of the constant velocity universal joints on theinboard side and the outboard side to equal dimensions, and forming theprotruding surface into the same shape on the inboard side and theoutboard side are also possible.

At least one of the cup member 12 a, 12 a ₁, or 12 a ₂ and the shaftmember 13 a or 13 b before the welding may be prepared as anintermediate component without performing heat treatment. In this case,the welding post-heating and finishing such as grinding andquenched-steel cutting work are performed after welding. Thus, thisconfiguration is suited to the cup members 12 a, 12 a ₁, and 12 a ₂ andthe shaft members 13 a and 13 b having such shapes and specificationsthat the hardness of the heat-treated portion may be affected bytemperature rise at the periphery due to heat generated during weldingafter heat treatment. The intermediate component is assigned with aproduct number for management.

Further, at least one of the cup member 12 a, 12 a ₁, or 12 a ₂ and theshaft member 13 a or 13 b before the welding may be prepared as afinished component subjected to heat treatment. The finished componentsubjected to heat treatment is a finished component subjected to theheat treatment and the finishing such as grinding after the heattreatment or quenched-steel cutting work. In this case, it is possibleto obtain the cup member 12 a, 12 a ₁, or 12 a ₂ prepared as thefinished component for common use for each joint size, and the shaftmembers having a variety of specifications of the shaft section for eachvehicle type. Thus, the cup members and the shaft members can each beassigned with a product number for management. Therefore, the cost issignificantly reduced through the standardization of a product type ofthe cup members 12 a, 12 a ₁, and 12 a ₂, and the burden of productionmanagement is significantly alleviated.

Further, the cup members 12 a, 12 a ₁, and 12 a ₂ prepared for commonuse and the shaft members 13 a and 13 b having a variety ofspecifications of the shaft section can be manufactured separately untilthe cup members and the shaft members are formed into the finishedcomponents subjected to the finishing such as forging, turning, heattreatment, grinding, and quenched-steel cutting work. Further, as wellas reduction of setups and the like, the enhancement of productivity isachieved. However, the cup members 12 a, 12 a ₁, and 12 a ₂ and theshaft members 13 a and 13 b as the finished components are not limitedto members subjected to finishing such as the grinding after the heattreatment or the quenched-steel cutting work as described above. The cupmembers 12 a, 12 a ₁, and 12 a ₂ and the shaft members 13 a and 13 bassuming a state after completion of heat treatment and before beingsubjected to the finishing are encompassed.

The effects of the above-mentioned embodiments of the present inventionare summarized and described below.

According to the embodiments, in the outer joint member 11, 11 ₂, or 11₂ of a constant velocity universal joint, the outer joint membercomprises, through use of separate members, the cup section 12 havingtrack grooves formed at an inner periphery of the cup section 12 andconfigured to allow the torque transmitting elements to roll thereon,and the shaft section 13 that extends from the bottom of the cup section12 in the axial direction. The cup member 12 a, 12 a ₁, or 12 a ₂forming the cup section 12 and the shaft member 13 a or 13 b forming theshaft section 13 are welded to each other.

The cup member 12 a, 12 a ₁, or 12 a ₂ and the shaft member 13 a or 13 bare made of medium to high carbon steel.

The cup member 12 a, 12 a ₁, or 12 a ₂ has a bottomed cylindrical shapethat is opened at one end, and comprises the cylindrical portion 12 a 1,12 a 1 ₁, or 12 a 1 ₂, the bottom portion 12 a 2, 12 a 2 ₁, or 12 a 2 ₂,and the short shaft section 12 a 3, 12 a 3 ₁, or 12 a 3 ₂ of a solidshaft shape protruding from the bottom portion and has the joining endsurface 50, 50 ₁, or 50 ₂ at an end portion.

The shaft member 13 a or 13 b has a solid shaft shape and has thejoining end surface 51 at one end thereof.

The joining end surface 50, 50 ₁, or 50 ₂ of the cup member 12 a, 12 a₁, or 12 a ₂ and the joining end surface 51 of the shaft member 13 a or13 b are brought into abutment against each other, and a high energyintensity beam is radiated from an outer side in the radial direction toform the welded portion 49. The structure of the molten metal 49 a atthe welded portion 49 is in a mixed phase of ferrite and granularcementite.

The molten metal 49 a of the welded portion 49 has a hardness of from280 HV to 380 HV. There is provided the microstructure from which thegranular cementite is precipitated, and hence the molten metal 49 a isharder than the case of not performing post-heating, and also hastoughness.

The manufacturing method according to the embodiments is a method ofmanufacturing the above-mentioned outer joint members 11, 11 ₁, and 11₂. The method comprises performing pre-heating before radiating a highenergy intensity beam for welding to input heat to the joining portion,and performing post-heating after welding to reduce the cooling rate forthe welded portion. Through employment of post-heating in addition topre-heating, the input heat of welding can be utilized in thepost-heating. Thus, the input heat amount can be secured with shortpre-heating time, and the entire welding cycle time can be reduced ascompared to the case of performing only pre-heating.

The pre-heating in the embodiments comprises heating the periphery ofthe joining end surface between the cup member and the shaft member forabout 15 seconds to raise the temperature from the normal temperature toabout 250° C.

The welding in the embodiments comprises, after pre-heating, raising thetemperature in the periphery of the welded portion welded portion fromabout 100° C. to a melting point of steel (about 1,600° C.) or higherfor about 6 seconds. The periphery of the welded portion is used becausethe temperature of the welded portion cannot be measured.

The post-heating in the embodiment comprises, after welding, at the timewhen the welded portion is rapidly cooled down to 450° C., raising thetemperature of the welded portion to about 600° C. and air-cooling thewelded portion.

The pre-heating, the post-heating, or both the pre-heating and thepost-heating may be performed through use of an electron gun which isthe same as the electron gun for use in welding, or may be performedthrough use of an electron gun other than the electron gun for use inwelding. The former is less expensive in equipment cost, and the lattermay be expected to further reduce the welding cycle time.

The embodiments of the present invention are described above withreference to the attached drawing. However, the present invention is notlimited to the embodiments described herein and illustrated in theattached drawings. The present invention can be carried out with variousmodifications within the range of not departing from the scope ofclaims.

The case of employing the electron beam welding is described as anexample. However, the present invention is applicable not only to thecase of the electron beam welding but also to the case of employinglaser welding or other welding through use of a high energy intensitybeam.

Further, the double-offset type constant velocity universal joint andthe tripod type constant velocity universal joint are exemplified as theplunging type constant velocity universal joint. However, the presentinvention is also applicable to an outer joint member of a cross-groovetype constant velocity universal joint or other plunging type constantvelocity universal joint, and to an outer joint member of a fixed typeconstant velocity universal joint. Further, the case of applying thepresent invention to the outer joint member of the constant velocityuniversal joint constructing a drive shaft is described as an example.However, the present invention is also applicable to an outer jointmember of a constant velocity universal joint constructing a propellershaft.

REFERENCE SIGNS LIST

-   10 plunging type constant velocity universal joint-   11, 11 ₁, 11 ₂ outer joint member-   12, 12 ₁, 12 ₂ cup section-   12 a, 12 a ₁, 12 a ₂ cup member-   12 a 1, 12 a 1 ₁, 12 a 1 ₂ cylindrical portion-   12 a 2, 12 a 2 ₁, 12 a 2 ₂ bottom portion-   12 a 3, 12 a 3 ₁, 12 a 3 ₂ short shaft section-   13 shaft section (long stem section)-   13 a, 13 b shaft member-   14 bearing mounting surface-   16 inner joint member-   17 tripod member-   19 torque transmitting element (roller)-   41 torque transmitting element (ball)-   49 welded portion-   49 a molten metal-   49 b heat-affected portion-   50, 50 ₁, 50 ₂ joining end surface of cup member-   51 joining end surface of shaft member-   100 welding apparatus-   120 ultrasonic flaw-detection apparatus

The invention claimed is:
 1. A method of manufacturing an outer jointmember of a constant velocity universal joint, the outer joint membercomprising: a cup section having track grooves formed at an innerperiphery of the cup section and configured to allow torque transmittingelements to roll thereon; and a shaft section formed at a bottom portionof the cup section, the outer joint member being constructed by formingthe cup section and the shaft section through use of separate members,and by welding a cup member forming the cup section and a shaft memberforming the shaft section, the cup member and the shaft member beingmade of medium to high carbon steel, the cup member having a bottomedcylindrical shape that is opened at one end, and comprising acylindrical portion, a bottom portion, and a shaft section of a solidshaft shape protruding from the bottom portion and having a joining endsurface at an end portion, the shaft member having a solid shaft shapeand having a joining end surface at one end thereof, the joining endsurface of the cup member and the joining end surface of the shaftmember being brought into abutment against each other, a high energyintensity beam being radiated from an outer side in a radial directionto form a welded portion, the method comprising: performing pre-heatingbefore radiating a high energy intensity beam for welding to input heatto a joining portion; and performing post-heating after welding toreduce a cooling rate for the welded portion by which a structure of amolten metal at the welded portion is formed to be in a mixed phase offerrite and granular cementite, wherein the post-heating is startedafter the welding when a temperature of the welded portion becomes lowerthan 530° C., and continues heating to a temperature less than atransformation point A₁.
 2. The method of manufacturing an outer jointmember of a constant velocity universal joint according to claim 1,wherein the pre-heating comprises heating a periphery of a joining endsurface between the cup member and the shaft member for about 15 secondsto raise a temperature from a normal temperature to about 250° C.
 3. Themethod of manufacturing an outer joint member of a constant velocityuniversal joint according to claim 2, wherein the pre-heating, thepost-heating, or both the pre-heating and the post-heating is performedwith an electron gun which is the same as the electron gun for use inthe welding.
 4. The method of manufacturing an outer joint member of aconstant velocity universal joint according to claim 2, wherein thepre-heating, the post-heating, or both the pre-heating and thepost-heating is performed with an electron gun other than an electrongun for use in the welding.
 5. The method of manufacturing an outerjoint member of a constant velocity universal joint according to claim1, wherein the welding comprises, after the pre-heating, raising atemperature in a periphery of the welded portion from about 100° C. to amelting point of steel or higher for about 6 seconds.
 6. The method ofmanufacturing an outer joint member of a constant velocity universaljoint according to claim 5, wherein the pre-heating, the post-heating,or both the pre-heating and the post-heating is performed with anelectron gun which is the same as the electron gun for use in thewelding.
 7. The method of manufacturing an outer joint member of aconstant velocity universal joint according to claim 5, wherein thepre-heating, the post-heating, or both the pre-heating and thepost-heating is performed with an electron gun other than an electrongun for use in the welding.
 8. The method of manufacturing an outerjoint member of a constant velocity universal joint according to claim1, wherein the post-heating comprises, after the welding, at a time whenthe welded portion is rapidly cooled down to 450° C., raising thetemperature of the welded portion to about 600° C. and air-cooling thewelded portion.
 9. The method of manufacturing an outer joint member ofa constant velocity universal joint according to claim 8, wherein thepre-heating, the post-heating, or both the pre-heating and thepost-heating is performed with an electron gun which is the same as theelectron gun for use in the welding.
 10. The method of manufacturing anouter joint member of a constant velocity universal joint according toclaim 8, wherein the pre-heating, the post-heating, or both thepre-heating and the post-heating is performed with an electron gun otherthan an electron gun for use in the welding.
 11. The method ofmanufacturing an outer joint member of a constant velocity universaljoint according to claim 1, wherein the pre-heating, the post-heating,or both the pre-heating and the post-heating is performed with anelectron gun which is the same as the electron gun for use in thewelding.
 12. The method of manufacturing an outer joint member of aconstant velocity universal joint according to claim 1, wherein thepre-heating, the post-heating, or both the pre-heating and thepost-heating is performed with an electron gun other than an electrongun for use in the welding.